1. Field of the Invention
The present invention relates generally to a laser apparatus, and more particularly to a solid-state laser apparatus using a lamp as laser excitation means, for providing iterative oscillatory outputs of pulsed laser beams.
2. Description of the Related Art
This type of solid-state laser apparatus typically allows a minute standby discharge current, a so-called simmer current, to flow through the excitation lamp during the standby periods (not oscillating laser) for the purpose of achieving an improved start of lighting of the excitation lamp upon the laser oscillation. The simmer current forms a discharge path within the excitation lamp despite the standby periods, so that an intrinsic lamp current for the lamp lighting (laser oscillation) can readily flow therethrough from the main laser power supply, making high-speed iterative pulse oscillations feasible.
As a result of investigations effected by the inventor, it has proved that upon the iterative oscillatory outputs of the pulsed laser beams, the simmer current may affect both the service life of the excitation lamp and the stability in the laser output. That is, it has turned out that a larger simmer current gives the excitation lamp a shorter service life, whereas a smaller simmer current renders the laser output more unstable upon the high-speed iterations.
Such a conventional solid-state laser apparatus has however employed the simmer current having a fixed current value irrespective of the repetition rate of the pulse oscillations. For this reason, there arose problems on occasions that the excitation lamp may become consumed at a relatively early stage even in the case of low pulse repetition rate operations at all times or of low ordinary operation rate or that the laser output may become unstable upon an increase in the pulse repetition rate.